Remarkably, only non-tumor BRAFV600E ATIIs showed an increment in p21CIP1 expression compared to both controls and adenoma ATIIs (Fig. 4D), thus indicating that the majority of p21CIP1-positive cells in adenomas are not SPC+ATIIs and that the oncogenic challenge elicits a rapid p21CIP1activation in ATIIs before they can give rise to adenomas (Supplementary Fig. 6A). Here, CDKN1A is linked to adenoma.